I've been using marvin for a couple of weeks now and I'm really enjoying it. After almost a year my iPad is finally starting to fulfill the task I bought the thing for.
As nice of as app it is however, I am finding it lacking in a few features that that prevents me from recommending it wholeheartedly. I've emailed Kris about them earlier, but I want to discuss one of those features here because I have not seen it mentioned it by anyone else.
It is about the way in which to get books to marvin. Marvin makes it easy to download books from Dropbox by it's in-app search. But it is still a manual process. I feel very strongly that this is not how the cloud should work at all. Synchronization with dropbox should be automatic. When I delete a book from dropbox (i.e. deleting it from calibre and having it removed from my calibre library that I sync to dropbox), it should disappear from marvin automatically. When I add a book in dropbox it should show up in marvin automatically. When I change the cover of a book in dropbox it should change in marvin automatically. When I add a tag to a book it should be updated in marvin automatically.
That is how the cloud should work. Why? Because people can have tons of books and its tough work organizing and controlling them all. I can't do it manually for every device I own. It's a nightmare.
For all the advantages that marvin has over reading systems like kindle and nook and kobo and google play books, this is one major area where it falls short. Every single one of those systems synchronizes your library (at least the ones bought from them) across your reading devices. Its the one thing they all get right. I wish marvin would do it too.